On Sep 21, 2012 4:09 PM, "Bala subramanian" <bala.biophys...@gmail.com> wrote: > > Friends, > May i know why do get a Valuerror if i check any value in a is between > 3.0 to 5.0 ? > >>> import numpy as np > >>> a=np.array([ 2.5, 2.6, 3.0 , 3.5, 4.0 , 5.0 ]) > >>> (a > 7).any() > False > >>> (a > 4).any() > True > >>> (3 < a < 5).any() > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > ValueError: The truth value of an array with more than one element is > ambiguous. Use a.any() or a.all()
You need to use ((3 < a) & (a <5)).any() The problem is not with any(). The problem is that the multiple binary comparison needs to convert its intermediate results to bool. So (3 < a < 5) is processed as: (3 < a) and (a < 5) To process the 'and' operator python needs to know if the first expression is True. This means calling bool(3 < a). But, since (3 < a) is an array of booleans it cannot be said to be True or False. This is what gives the ValueError that you see. If you use bitwise-and '&' instead of logical-and 'and' it will perform the and operation separately on each element of each array which is what you want. Oscar
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